add more specific ExecutableNotFound exception

CHANGES

@@ -7,6 +7,9 @@ Version 0.7.1 (in development)
 
 Fix graphivz.view exception on unsupported platform.
 
+Raise a dedicated RuntimeError subclass graphviz.ExecutableNotFound when the
+Graphviz executables are not found.
+
 
 Version 0.7
 -----------

docs/api.rst

@@ -61,3 +61,6 @@ Other
 
 .. autodata:: graphviz.FORMATS
    :annotation:
+
+.. autodata:: graphviz.ExecutableNotFound
+   :annotation:

graphviz/__init__.py

@@ -26,13 +26,14 @@
 
 from .dot import Graph, Digraph
 from .files import Source
-from .backend import render, pipe, view, ENGINES, FORMATS
+from .backend import render, pipe, view, ENGINES, FORMATS, ExecutableNotFound
 
 __all__ = [
     'Graph', 'Digraph',
     'Source',
     'render', 'pipe', 'view',
     'ENGINES', 'FORMATS',
+    'ExecutableNotFound',
 ]
 
 __title__ = 'graphviz'
@@ -46,3 +47,5 @@
 
 #: Set of known output formats for rendering ('pdf', 'png', ...)
 FORMATS = FORMATS
+
+ExecutableNotFound = ExecutableNotFound

graphviz/backend.py

@@ -64,6 +64,16 @@
     STARTUPINFO.wShowWindow = subprocess.SW_HIDE
 
 
+class ExecutableNotFound(RuntimeError):
+    """Exception raised if the Graphviz executable is not found."""
+
+    _msg = ('failed to execute %r, '
+            'make sure the Graphviz executables are on your systems\' PATH')
+
+    def __init__(self, args):
+        super(ExecutableNotFound, self).__init__(self._msg % args)
+
+
 def command(engine, format, filepath=None):
     """Return args list for subprocess.Popen and name of the rendered file."""
     if engine not in ENGINES:
@@ -90,7 +100,7 @@ def render(engine, format, filepath):
         The (possibly relative) path of the rendered file.
     Raises:
         ValueError: If engine or format are not known.
-        RuntimeError: If the Graphviz executable is not found.
+        graphviz.ExecutableNotFound: If the Graphviz executable is not found.
         subprocess.CalledProcessError: If the exit status is non-zero.
     """
     args, rendered = command(engine, format, filepath)
@@ -99,9 +109,7 @@ def render(engine, format, filepath):
         subprocess.check_call(args, startupinfo=STARTUPINFO)
     except OSError as e:
         if e.errno == errno.ENOENT:
-            raise RuntimeError('failed to execute %r, '
-                'make sure the Graphviz executables '
-                'are on your systems\' path' % args)
+            raise ExecutableNotFound(args)
         else:  # pragma: no cover
             raise
 
@@ -120,7 +128,7 @@ def pipe(engine, format, data, quiet=False):
         Binary (encoded) stdout of the layout command.
     Raises:
         ValueError: If engine or format are not known.
-        RuntimeError: If the Graphviz executable is not found.
+        graphviz.ExecutableNotFound: If the Graphviz executable is not found.
         subprocess.CalledProcessError: If the exit status is non-zero.
     """
     args, _ = command(engine, format)
@@ -131,9 +139,7 @@ def pipe(engine, format, data, quiet=False):
             startupinfo=STARTUPINFO)
     except OSError as e:
         if e.errno == errno.ENOENT:
-            raise RuntimeError('failed to execute %r, '
-                'make sure the Graphviz executables '
-                'are on your systems\' path' % args)
+            raise ExecutableNotFound(args)
         else:  # pragma: no cover
             raise
 

graphviz/files.py

@@ -92,7 +92,7 @@ def pipe(self, format=None):
             Binary (encoded) stdout of the layout command.
         Raises:
             ValueError: If `format` is not known.
-            RuntimeError: If the Graphviz executable is not found.
+            graphviz.ExecutableNotFound: If the Graphviz executable is not found.
             subprocess.CalledProcessError: If the exit status is non-zero.
         """
         if format is None:
@@ -145,7 +145,7 @@ def render(self, filename=None, directory=None, view=False, cleanup=False):
         Returns:
             The (possibly relative) path of the rendered file.
         Raises:
-            RuntimeError: If the Graphviz executable is not found.
+            graphviz.ExecutableNotFound: If the Graphviz executable is not found.
             subprocess.CalledProcessError: If the exit status is non-zero.
             RuntimeError: If viewer opening is requested but not supported.
         """
@@ -171,7 +171,7 @@ def view(self, filename=None, directory=None, cleanup=False):
         Returns:
             The (possibly relative) path of the rendered file.
         Raises:
-            RuntimeError: If the Graphviz executable is not found.
+            graphviz.ExecutableNotFound: If the Graphviz executable is not found.
             subprocess.CalledProcessError: If the exit status is non-zero.
             RuntimeError: If opening the viewer is not supported.
 

tests/test_backend.py

@@ -4,7 +4,8 @@
 
 import pytest
 
-from graphviz.backend import render, pipe, view, STARTUPINFO
+
+from graphviz.backend import render, pipe, view, ExecutableNotFound, STARTUPINFO
 
 
 def test_render_engine_unknown():
@@ -20,7 +21,7 @@ def test_render_format_unknown():
 
 
 def test_render_missingdot(empty_path):
-    with pytest.raises(RuntimeError) as e:
+    with pytest.raises(ExecutableNotFound) as e:
         render('dot', 'pdf', '')
     e.match(r'execute')
 
@@ -31,14 +32,18 @@ def test_render_missingfile():
     assert e.value.returncode == 2
 
 
-def test_render_mock(check_call):
+def test_render_mocked(check_call):
     assert render('dot', 'pdf', '') == '.pdf'
     check_call.assert_called_once_with(['dot', '-Tpdf', '-O', ''],
                                        startupinfo=STARTUPINFO)
 
 
+def test_render(check_call):
+    pass  # TODO
+
+
 def test_pipe_missingdot(empty_path):
-    with pytest.raises(RuntimeError) as e:
+    with pytest.raises(ExecutableNotFound) as e:
         pipe('dot', 'pdf', b'')
     e.match(r'execute')
 
@@ -49,7 +54,7 @@ def test_pipe_invalid_data():
     assert e.value.returncode == 1
 
 
-def test_pipe_mock(Popen):
+def test_pipe_mocked(Popen):
     pass  # TODO